Relation between electron scattering resonances of isolated NTCDA molecules and maxima in the density of unoccupied states of condensed NTCDA layers

The empty-level structure of the 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) molecule is characterized by means of dissociative electron attachment (DEA) experiments in the gas phase coupled with DFT calculations. Distinct maxima in the anion currents generated by electron attachment to NTCDA, as a function of incident electron energy, are ascribed to capture of incident electrons into empty orbitals, i.e., the process referred to as shape resonance. The empty orbital energies of gas-phase NTCDA shifted to 1.2 eV lower energy reproduce satisfactorily the maxima of the unoccupied electronic states of a multilayer NTCDA film measured by means of the very low energy electron diffraction method and the total current spectroscopy measurement scheme. The present results indicate that the empty levels of individual NTCDA molecules are stabilized in the solid state, but their relative energies remain nearly unaltered. The stabilization energy in multilayer film of NTCDA molecules is likely due to attractive polarization forces. Fragmentation of the gas-phase NTCDA temporary parent anions via the DEA mechanism, the other issue of the present investigation, leads to the rupture of the bonds between the end carbonyl groups and the naphthalene core, and occurs at incident electron energies above 2 eV. Possible chemical changes in condensed NTCDA molecules initiated by the DEA mechanism under conditions of electron transport through the film are discussed.